RUSBF135 Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUSBF135 is a polymeric PTC resettable fuse manufactured by Littelfuse, part of the PolySwitch® series. This through-hole radial disc component provides overcurrent protection with a hold current of 1.35 A and trip current of 2.7 A at a maximum voltage rating of 16V. The device is designed for applications requiring automatic reset functionality after fault conditions are cleared. As an active product with full compliance certifications, substitute parts may be required due to inventory availability, lead time constraints, or specific application voltage requirements.

Substiute Parts

RUSBF135

LittelfuseIn Stock: 941RUSBF135 Datasheet

Current PartRFQ

MF-R135

Bourns Inc.In Stock: 2443MF-R135 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the RUSBF135 is determined by strict adherence to the following electrical and mechanical parameters:

Critical Substitution Parameters:

• Current - Hold (Ih) (Max): Must equal 1.35 A
• Current - Trip (It): Must equal 2.7 A
• Mounting Type: Must be Through Hole
• Package / Case: Must be Radial, Disc
• Lead Spacing: Must be compatible (0.199" ± tolerance)

Voltage Consideration: The RUSBF135 operates at a maximum voltage of 16V. Substitute parts with higher voltage ratings (such as 30V) are electrically compatible in 16V applications, as they provide equivalent or superior voltage withstand capability. However, substitute parts with lower voltage ratings are not acceptable.

Resistance Parameters: Initial and post-trip resistance values must fall within acceptable ranges to ensure circuit protection performance. Variations in these parameters are acceptable provided the hold and trip current specifications remain unchanged.

The MF-R135 (Bourns Inc., Multifuse® series) meets all critical substitution criteria with identical hold and trip current ratings, compatible mounting and package specifications, and higher voltage rating suitable for 16V applications.

Parameter Comparison

Engineering Selection Recommendations

RUSBF135 (Littelfuse PolySwitch®): Select this part for applications where UL certification is a specific requirement. The RUSBF135 carries UL approval in addition to CSA and TUV certifications. This part is active and in stock with 873 units available.

MF-R135 (Bourns Inc. Multifuse®): Select this part as a substitute when RUSBF135 availability is constrained. The MF-R135 provides identical hold and trip current performance with a higher voltage rating (30V), making it suitable for 16V applications. This part carries cURus and TUV certifications and is available in bulk packaging with 2400 units in stock. The MF-R135 is active and ROHS3 compliant.

Both parts are polymeric PTC resettable fuses with active product status and full RoHS3 compliance. Selection between them should be based on certification requirements, packaging preference, and inventory availability.

Frequently Asked Questions (FAQ)

Q: Can the MF-R135 replace the RUSBF135 in a 16V circuit? A: Yes. The MF-R135 has a 30V maximum voltage rating, which exceeds the 16V requirement of the RUSBF135. The hold current (1.35 A) and trip current (2.7 A) are identical, ensuring equivalent protection performance.

Q: What is the significance of the different time-to-trip values (4.5 s vs. 7.3 s)? A: The time-to-trip parameter indicates how quickly the fuse responds to overcurrent conditions. The RUSBF135 trips in 4.5 seconds while the MF-R135 trips in 7.3 seconds. Both values are within acceptable ranges for polymeric PTC resettable fuses. Application-specific requirements should determine if this difference is acceptable.

Q: Are the lead spacing differences (0.199" vs. 0.201") significant? A: The lead spacing difference of 0.002" (0.05mm) is negligible for through-hole PCB applications. Both parts are compatible with standard 5mm pitch footprints used for radial disc components.

Q: What is the difference between bulk and bag packaging? A: Bag packaging (RUSBF135) is typically used for smaller quantities and individual component handling. Bulk packaging (MF-R135) is used for higher-volume orders. Both packaging types contain the same component specifications and performance characteristics.

Q: Why do the initial and post-trip resistance values differ between these parts? A: Resistance variations are inherent to different manufacturers' polymeric PTC formulations. The RUSBF135 has lower initial resistance (40 mOhms) compared to the MF-R135 (65 mOhms). These differences do not affect the hold and trip current performance, which are the primary protection parameters.

Q: Are both parts RoHS3 compliant? A: Yes. Both the RUSBF135 and MF-R135 are ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements.